Method of producing master and working pattern plates for etching and photolithographic apparatus therefor

ABSTRACT

In a method of producing master and working pattern plates for etching to form a shadow mask, various etching patterns are needed, for example, a pattern of predetermined holes for passing electron beams, a pattern of register marks necessary for accurate alignment of a pair of obverse and reverse working pattern plates, and a frame pattern for cutting off a portion which is to be a shadow mask from a metal plate by etching process. These individual pattern data required for etching are first prepared and then subjected to logical operation to prepare data representative of a synthetic pattern which is to be finally drawn on a photosensitive plate. Then, all the necessary patterns, including the frame pattern, register mark pattern, hole pattern, etc., are formed by continuous and collective exposure process by use of the synthetic pattern data, thereby eliminating the need for the step of aligning the individual patterns by a manual operation, which has heretofore been essential for multiple exposure, and thus solving not only the conventional problems in terms of both quality and process but also the problem attributable to the positioning accuracy of a photolithographic apparatus in which control is effected by a laser interferometric measuring device in an environment other than a vacuum.

This is a divisional of application Ser. No. 08/067,340 filed on May 25,1993, now U.S. Pat. No. 5,500,326, which is a continuation ofapplication Ser. No. 07/666,351, filed Mar. 8, 1991, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a method of producing pattern platesfor etching. More particularly, the present invention relates to amethod of producing a pair of obverse and reverse working pattern platesfor use in the manufacture of etched products such as shadow masks forcolor picture tubes, lead frames for semiconductor devices, etc., and apair of obverse and reverse master pattern plates used to produce suchworking pattern plates. The present invention further relates to aphotolithographic apparatus which may be employed to carry out theabove-described pattern plate producing method.

Etched products such as shadow masks are generally produced by exposinga metal plate having a resist coated over the obverse and reverse sidesthereof through a pair of obverse and reverse working pattern plates foretching each formed with a predetermined etching pattern, the workingpattern plates being in close contact with the two sides of the metalplate, and developing the resist to form resist patterns on the obverseand reverse sides of the metal plate, and then etching the two sides ofthe plate formed with the respective resist patterns.

Working pattern plates which are used in the actual etching process areproduced by use of original pattern plates, which are known as masterpattern plates. More specifically, a pair of obverse and reverse masterpattern plates are first produced, and then working pattern plates areproduced by use of the respective master pattern plates. Forexperimental etching or small-scale production, a photosensitive glassplate having the required pattern formed thereon by a photolithographicmachine may be used directly as a working pattern plate. In the case ofmass production, for example, it is common practice to produce workingpattern plates by use of master pattern plates and use the workingpattern plates in etching process carried out along a production line.

In general, of the two working pattern plates, one which has a holepattern with a larger diameter is called "obverse working patternplate", and the other "reverse working pattern plate".

In the production of a pair of obverse and reverse pattern plates, ithas been conventional practice to divide all the patterns required foretching into a plurality of discrete patterns, i.e., a pattern of marksused in the alignment of a pair of obverse and reverse pattern plates(these alignment marks will hereinafter be referred to as "registermarks"), a frame pattern, a pattern of holes, etc., and to form thesepatterns on a single photosensitive plate in the form of a syntheticpattern by partial exposure or multiple exposure, as disclosed, forexample, in Japanese Patent Post-Examination Publication Nos. 63-19860and 63-19861 (1988).

However, the above-described conventional method requires a great dealof time and labor to carry out the operation since it is necessary toeffect multiple exposure with a plurality of discrete pattern platesbeing successively brought into contact with a single photosensitiveplate.

Because in the etching process along a production line a pair of obverseand reverse working pattern plates are brought into close contact withboth sides of a steel plate which are coated with a resist, the twoworking pattern plates are formed with register mark patterns to alignthe positions of the obverse and reverse etching patterns relative toeach other. Hitherto, since the obverse and reverse master patternplates are formed by multiple exposure, when each master pattern plateis formed, the relative position of the patterns to be formed into asynthetic pattern may change due to a manual operation, which gives riseto a problem in terms of quality, that is, nonuniformity in the qualityof the products.

In addition, no matter which of various known photolithographicapparatuses is used to write etching patterns, the resulting patternsinvolve various distortions, more or less, i.e., a distortion inorthogonality, that is, an error in which an angle which should be aright angle is deviated therefrom, or a distortion in length, that is,an error in which a length becomes longer or shorter than the designedone. Thus, any etching pattern that is written on an original patternplate has some distortions; under certain circumstances, distortions maybe present everywhere on a single original plate. The tendency ofdistortions is the same for all patterns that are written by the samephotolithographic apparatus under the same conditions. Accordingly, ifthe same photolithographic apparatus is used to produce a pair ofobverse and reverse original pattern plates and etching is effected byuse of working pattern plates that are produced on the basis of theseoriginal plates, distortions that are produced by this photolithographicapparatus will double.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method ofproducing master and working pattern plates for etching in which all thepatterns required for etching are synthesized together in the form ofdata to form synthetic pattern data and a photosensitive plate issubjected to continuous and collective exposure by use of the syntheticpattern data, thereby solving the problems of the prior art, that is, anundesired change in the relative position of individual patterns and thenonuniformity of quality due to the conventional manual operation, andalso simplifying the operation process.

It is another object of the present invention to provide aphotolithographic apparatus which may be effectively used to carry outthe above-described method of producing master and working patternplates for etching.

In the present invention, pattern data which are needed to produce ashadow mask, for example, by etching, i.e., data about a pattern ofregister marks, a pattern of predetermined holes and a frame pattern,are prepared, and these individual pattern data are subjected to logicaloperation to prepare synthetic pattern data, and then continuous andcollective exposure is effected with a photolithographic apparatus byuse of the synthetic pattern data to produce a master pattern plate,thereby solving the problems such as an undesired change in the relativeposition of individual patterns, i.e., the frame pattern, register markpattern, hole pattern, etc., and the nonuniformity of quality due to theconventional manual operation, and also simplifying the process ofproducing a shadow mask or other etched product.

More specifically, various etching patterns are needed to produce ashadow mask, i.e., a pattern of predetermined holes for passing electronbeams, a pattern of register marks for accurate alignment of a pair ofobverse and reverse working pattern plates, and a frame pattern forcutting off a portion which is to be a shadow mask from a metal plate byetching process. In the present invention, data representative of theseindividual patterns required for etching are first prepared and thensubjected to logical operation to prepare data representative of asynthetic pattern which is to be finally drawn on a photosensitiveplate, such as that shown in FIG. 2. Then, all the necessary patterns,including the frame pattern, register mark pattern, hole pattern, etc.,are formed by continuous and collective exposure process by use of thesynthetic pattern data, thereby eliminating the need for the step ofaligning the individual patterns by a manual operation, which hasheretofore been essential for multiple exposure, and thus solving theconventional problems in terms of both quality and process. It should benoted that, in FIG. 2, a, b and c denote a register mark pattern, aframe pattern and a hole pattern, respectively.

To cope with distortions that are generated due to the mechanicalaccuracy of the photolithographic apparatus employed, one of the pair ofobverse and reverse patterns, e.g., the obverse pattern, is subjected toreversal development in a desired step, thereby obtaining a desiredblack-and-white, i.e., positive-negative, condition for the obverse andreverse patterns and setting the direction of each pattern in a propercondition to enable distortions of the obverse and reverse patterns dueto the photolithographic apparatus to cancel each other.

Thus, according to the production method of the present invention, allthe etching patterns needed to produce a shadow mask or other etchedproduct are synthesized together in the form of data and continuous andcollective exposure is effected by use of the synthetic pattern data toproduce a pattern plate. There is therefore no need for the conventionalmultiple exposure process. Thus, it is possible to eliminate the needfor the time and labor which would otherwise be required for themultiple exposure process and to solve the problems accompanying themultiple exposure process.

As a photolithographic apparatus which may be used to carry out theabove-described method of producing master and working pattern platesfor etching, the present invention provides a photolithographicapparatus of the type having a device that controls the movement of amoving mirror of a Michelson interferometer from its origin by countingthe number of interference fringes, or Doppler shift frequency, from theinterferometer with a counter, thereby controlling the relative positionof an exposure head and a photosensitive plate, the apparatus comprisinga position controller that sets the origin of the moving mirror at adistance from a beam splitter of the Michelson interferometer, moves themoving mirror to the origin to reset the count of the counter to zeroand then feedback-controls the position of the moving mirror on thebasis of the difference between a value obtained by multiplying thecount of the counter by the wavelength in the air at the present timeand a target position of the moving mirror, the position controllerhaving a memory means for storing the wavelength in the air at the timewhen the moving mirror is moved to the origin and the counter is resetto zero, and the position controller being arranged such that a valueobtained by dividing the distance between the beam splitter and theorigin by the wavelength stored in the memory means is added to thecount of the counter; the resulting sum is multiplied by the wavelengthin the air at the present time; the distance between the beam splitterand the origin is subtracted from the resulting product; and theposition of the moving mirror is feedback-controlled on the basis of thedifference between the result of the subtraction and a target positionof the moving mirror.

With the above-described photolithographic apparatus, even if thewavelength changes due to a change in the pressure, temperature orhumidity of the air in the dead path between the beam splitter and theorigin, the position error due to the wavelength change is corrected, sothat, even if there is a change in the atmospheric pressure, temperatureor humidity of the environment of the photolithographic apparatus, noirregularities will occur on the resulting master pattern plate. Inaddition, since all the necessary patterns are formed by collectiveexposure process by use of the synthetic pattern data, the accuracy ofthe relative position of the individual patterns becomes extremely high.

The photolithographic apparatus used to carry out the above-describedproduction method may comprise a position controller that sets theorigin of the moving mirror at a distance from a beam splitter of theMichelson interferometer, moves the moving mirror to the origin to resetthe count of the counter to zero and then feedback-controls the positionof the moving mirror on the basis of the difference between the count ofthe counter and a value obtained by dividing a target position of themoving mirror by the wavelength in the air at the present time, theposition controller having a memory means for storing the wavelength inthe air at the time when the moving mirror is moved to the origin andthe counter is reset to zero, and the position controller being arrangedsuch that the distance between the beam splitter and the origin is addedto a target position of the moving mirror; the resulting sum is dividedby the wavelength in the air at the present time; and the position ofthe moving mirror is feedback-controlled on the basis of the differencebetween the resulting quotient and a value that is obtained by adding tothe count of the counter a value obtained by dividing the distancebetween the beam splitter and the origin by the wavelength stored in thememory means.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction,combinations of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) are flowcharts showing a first embodiment of theproduction method according to the present invention;

FIG. 2 is a view employed to explain synthetic pattern data;

FIGS, 3(a) and 3(b) illustrate the difference in size between registermark patterns drawn on a pair of obverse and reverse patterns;

FIGS. 4(a) and 4(b) are flowcharts showing a second embodiment of theproduction method according to the present invention;

FIGS. 5(a) and 5(b) are flowcharts showing a third embodiment of theproduction method according to the present invention;

FIG. 6 is a fragmentary perspective view of a photolithographicapparatus for forming shadow mask patterns;

FIG. 7 shows an optical arrangement of one example of a Michelsoninterferometer;

FIG. 8 is a block diagram of one example of the exposure head positioncontrol system in the conventional photolithographic apparatus forforming shadow mask patterns;

FIG. 9 is a block diagram of another example of the exposure headposition control system according to the prior art;

FIGS. 10(a) and 10(b) show shadow mask pattern writing conditions andirregularities generated under these conditions;

FIGS. 11(a) and 11(b) are views employed to explain a dead path;

FIG. 12 is a block diagram of a position controller in one embodiment ofthe photolithographic apparatus according to the present invention;

FIG. 13 is a block diagram of a position controller in anotherembodiment of the photolithographic apparatus according to the presentinvention; and

FIG. 14 is a schematic view of an arrangement in which a part of thephotolithographic apparatus is placed in a vacuum.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the method of producing master and working pattern platesfor etching according to the present invention will first be describedbelow with reference to the accompanying drawings.

Prior to the description of the embodiments, definitions of terms usedin this application will be given below. As a photosensitive materialthat is coated on a glass plate, a silver halide emulsion is used. Theterm "positive pattern" is herein employed to mean a pattern plate whichis formed in such a manner that hole and frame patterns are digitized toprepare pattern writing data; the patterns are drawn on a photosensitiveplate by exposure on the basis of the pattern writing data; and thepatterned portions are blackened directly or by contact exposure to forma synthetic pattern. In contrast, when the patterned portions arewhitened directly or by contact exposure, the resulting pattern plate isreferred to as a negative pattern. In other words, a pattern in whichthe portions digitized and exposed by a photolithographic apparatus areblackened is referred to as a positive pattern, whereas, a pattern inwhich the patterned portions are whitened is referred to as a negativepattern. On the other hand, as for register marks, a pattern which isdrawn by digitizing the inside of it, as shown in FIG. 3(a), is referredto as a positive pattern, whereas, a pattern which is drawn bydigitizing the area surrounding a register mark, as shown in FIG. 3(b),is referred to as a negative pattern.

In this application, the term "developing process" means ordinarydevelopment that is applied to a silver halide emulsion. Accordingly, inthe developing process the exposed portions are blackened. In contrast,the term "reversal development" means a developing process in which theblack-and-white relationship in a pattern is maintained as it is. Inother words, reversal development blackens the unexposed portions. Itshould be noted that the reversal development by the printing processexplained hereinafter is described, for example, in Japanese PatentLaid-Open (KOKAI) No. 55-164829 (1980), or Photographic Society ofJapan, "Elements of Photographic Engineering--Silver HalidePhotography," Corona-sha, Jan. 30, 1979, pp. 341-342.

A first embodiment will be explained below with reference to FIGS. 1(a)and 1(b).

FIGS. 1(a) and 1(b) are flowcharts respectively showing processes ofproducing an obverse working pattern plate and a reverse working patternplate, which are used in a pair.

In Step S1, frame pattern data, hole pattern data, register pattern dataand so forth for an obverse working pattern plate are preparedseparately. In this example, as for register marks, negative data isprepared, whereas, as for the other patterns, positive data is prepared.Then, as for each data, positive data is the data which is prepared bydigitizing the pattern area. Especially, as for register marks, positivedata is prepared by digitizing the oblique line portions shown in FIG.3(a), and negative data is prepared by digitizing the oblique lineportions shown in FIG. 3(b). Similarly, as for frame pattern, data forpositive data is prepared by digitizing the frame pattern area, and asfor hole pattern, data for positive data is prepared by digitizing thehole pattern area.

In Step S2, the individual pattern data prepared in Step S1 aresubjected to logical operation to prepare synthetic pattern data fromthese pattern data. At this time, the positional relationship betweenthe patterns must be established as designed, as a matter of course.

In Step S3, patterns are drawn continuously and collectively on aphotosensitive glass plate, for example, by a photolithographicapparatus (described later) according to the present invention and byuse of the synthetic pattern data obtained in Step S2, thereby forming alatent image corresponding to the synthetic pattern data. Thereafter,developing process is carried out in Step S4. Thus, a first obversepositive pattern plate is obtained.

In Step S5, contact exposure is effected by use of the first obversepositive pattern plate obtained in Step 4, and developing process iscarried out in Step S6, thus obtaining a first obverse negative patternplate, which is defined as an obverse master pattern plate.

Next, contact exposure is effected in Step S7 by use of the obversemaster pattern plate obtained in Step S6, and developing process iscarried out in Step S8, thus obtaining a second obverse positive patternplate, which is defined as an obverse working pattern plate.

As for the reverse pattern, frame pattern data, hole pattern data,register pattern data and so forth for reverse pattern plates are firstprepared separately in Step S11. Here, as for the patterns other thanthe register marks, data for positive patterns is prepared in the sameway as in the case of the obverse pattern plates, whereas, as for theregister marks, data for positive patterns is prepared. The reason forthis is to facilitate the alignment of a pair of obverse and reverseworking pattern plates in etching process carried out along a productionline by forming a negative register pattern on one of the two workingpattern plates and a positive register pattern on the other.

Steps S12 to S18 subsequent to the above are the same as Steps S2 to S8in the process of producing the obverse working pattern plate: That is,by the developing process in Step S16, a reverse master pattern plate isobtained; and by the developing process in Step S18, a reverse workingpattern plate is obtained.

It will be apparent that the patterns of the register marks on theobverse and reverse pattern plates are not necessarily limited tocross-shaped patterns such as those shown in FIGS. 3(a) and 3(b) andthat any desired patterns, for example, circular patterns or acombination of circular and cross-shaped patterns, may be employed aslong as the employed patterns facilitate the alignment of the obverseand reverse pattern plates. Negative-positive relation of the registermarks on the obverse and reverse patterns is determined so that theblack-and-white conditions of the obverse and reverse working patternplates are reverse to each other.

However, the register patterns on the obverse and reverse pattern platesneed to be different in size from each other. For example, assuming thatthe register patterns on the two pattern plates are such as those shownin FIGS. 3(a) and 3(b), respectively, the line width W₂ of the negativepattern shown in FIG. 3(b) is made larger than the line width W₁ of thepositive pattern shown in FIG. 3(a). Thus, the operator can recognizeclearly the relative position of the obverse and reverse patterns andhence conduct the alignment even more accurately. To provide adifference in the register pattern size between the obverse and reversepatterns, the line widths of the positive and negative patterns may bemade different from each other in the stage of the individual patterns.However, it is possible to attain the purpose even more readily bysetting the exposure light energy for the register pattern on either oneof the obverse and reverse patterns to be larger or smaller than thatfor the register pattern on the other. Since the method of controllingthe size of the register patterns during the exposure process is a knownmatter, detailed description thereof is omitted. It should be noted thatthe difference between W₁ and W₂ may be on the order of from several μmto several tens of μm. The control of the size of the register patternsmay be carried out in any exposure step, but it is preferably conductedin the step of producing a master pattern plate in Step S5 or S15.

In the case of small-scale production, a single working pattern platewill suffice for each of the obverse and reverse patterns; therefore,positive pattern plates that are obtained in Steps S4 and S14 may beused as working pattern plates directly, as a matter of course.

Although in the above-described embodiment patterns that are necessaryfor a pair of obverse and reverse pattern plates are only hole, frameand register patterns for simplification of the explanation, it is amatter of course that any other necessary patterns can be synthesized inthe stage of individual pattern data to produce obverse and reversemaster and working pattern plates in the same way as the above.

Next, a second embodiment will be explained with reference to FIGS. 4(a)and 4(b).

Although obverse and reverse master and working pattern plates can beproduced by the method described above, distortions are produced duringthe exposure process by the photolithographic apparatus, as statedabove, and it is therefore necessary to compensate for thesedistortions. In the present invention, the compensation for thedistortions is made by applying reversal development to either theobverse or reverse pattern.

FIG. 4(a) is a flowchart showing a production process that is carriedout when an obverse pattern is subjected to reversal development.

First, in Step S21, individual pattern data for an obverse pattern plateare prepared separately. In this example, as for register marks, datafor positive patterns is prepared, and as for the other patterns, datafor positive patterns is also prepared.

Thereafter, synthetic pattern data is prepared in Step S22, andcontinuous and collective exposure is effected with thephotolithographic appatatus by use of the synthetic pattern data to forma latent image corresponding to the synthetic pattern data (Step S23),and then developing process is carried out (Step S24), thus obtaining afirst obverse positive pattern plate.

Next, contact exposure is effected with the first obverse positivepattern plate (Step S25), and in Step S26, ordinary developing processis carried out for the register pattern portions, whereas, reversaldeveloping process is conducted for the pattern portions other than theregister pattern portions, thus obtaining a second obverse positivepattern plate.

Next, contact exposure is effected with the second obverse positivepattern plate (Step S27), and developing process is carried out (StepS28), thus obtaining a first obverse negative pattern plate, which isdefined as an obverse master pattern plate. Next, with the obversemaster pattern plate, contact exposure is effected (Step S29), anddeveloping process is carried out (Step S30), thus obtaining a thirdobverse positive pattern plate, which is defined as an obverse workingpattern plate.

FIG. 4(b) shows a method of producing a reverse working pattern plate,in which Steps S31 to S38 are the same as the corresponding steps shownin FIG. 1(b). However, individual pattern data which are prepared inStep S31 are such that, as for register marks, data for positivepatterns is prepared, and as for the other patterns, data for positivepatterns is also prepared, in the same way as in the case of data forobverse pattern plates prepared in Step S21.

The obverse and reverse working pattern plates obtained by theabove-described process are opposite to each other in theblack-and-white relationship in the register patterns. For the otherpatterns, the distortions produced by the photolithographic apparatusappear in the opposite directions to each other on the two workingpattern plates. Accordingly, the distortions can be canceled byemploying the pair of obverse and reverse working plate patterns.

A third embodiment will next be explained. In the second embodiment, asecond obverse positive pattern is obtained by reversal developmentcarried out after a first obverse positive pattern plate has beenobtained. This method is advantageous for the management of plates, butit has the disadvantage of necessitating a relatively large number ofsteps. In this embodiment, therefore, a description will be given abouta method by which the number of steps is reduced.

FIGS. 5(a) and 5(b) are flowcharts respectively showing processes ofproducing an obverse working pattern plate and a reverse working patternplate, which are used in a pair. The process of producing a reverseworking pattern plate is the same as that shown in FIG. 4(b). As for theobverse pattern, Steps S41 to S43 are the same as Steps S21 to S23 inFIG. 4(a). In this embodiment, however, after the continuous andcollective exposure, the register pattern portion is subjected toordinary developing process, whereas the other pattern portions aresubjected to reversal development (Step S44). Thus, a negative patternplate is obtained, which is defined as an obverse master pattern plate.

Thereafter, contact exposure is effected (Step S45), and developingprocess is carried out (Step S46), thus obtaining a first obversepositive pattern plate, which is defined as an obverse working patternplate.

As will be readily understood by a comparison between FIGS. 4(a) and5(a), it is apparent that this embodiment enables a reduction in thenumber of steps.

Although in the above-described embodiments reversal development iscarried out for the obverse pattern, it will be apparent that reversaldevelopment may be carried out for the reverse pattern.

In addition, this embodiment is the same as the first embodiment in thata difference is made in the register pattern size between the obverseand reverse patterns.

Although some embodiments of the method of producing master and workingpattern plates for etching have been described above, it should be notedthat the present invention is not necessarily limited to the describedembodiments and that various modifications may be imparted thereto. Forexample, although in the foregoing embodiments a silver halide emulsionis used as a photosensitive material, a negative photoresist comprisinga polymeric material may be employed instead. It is also possible toemploy a positive photoresist comprising a polymeric material; in such acase, the black-and-white relationship in each pattern data should bereversed.

As will be clear from the foregoing description, according to the methodof producing master and working pattern plates for etching of thepresent invention, all patterns required for etching are synthesizedtogether in the form of data, and a photosensitive plate is subjected tocontinuous and collective exposure by use of the synthetic pattern data.It is therefore possible to solve the problems in terms of quality ofthe prior art, i.e., an undesired change in the relative position ofindividual patterns and nonuniformity in quality of the products, andalso possible to simplify the operation process.

In addition, distortions that are produced by the photolithographicapparatus can be compensated for by incorporating a reversal developmentprocess into an appropriate step before the step of producing a workingpattern plate.

The following is a description of the photolithographic apparatus thatis employed in the exposure process explained in connection with FIGS.1(a), 1(b), 2, 3(a), 3(b), 4(a), 4(b), 5(a) and 5(b).

Prior to the description of the photolithographic apparatus according tothe present invention, a conventional photolithographic apparatus willbe explained.

With the recent development of extended definition TV and displaydevices for computer graphics, shadow masks for use in these deviceshave been demanded to have higher quality. The quality of shadow masksgreatly depends on the quality of master pattern plates that areemployed in the manufacture thereof. Accordingly, the degree of accuracyof a pair of obverse and reverse master pattern plates decides thequality of the resulting shadow masks. In the method of producing masterand working pattern plates for etching, irregularities which are broughtabout by the photolithographic apparatus constitute an obstacle toproduction of highly accurate master pattern plates. The irregularitiesoccur due to a lowering in the positional accuracy of small holepatterns which should be arranged regularly. It is essential to checkthe lowering in the positional accuracy in order to produce shadow maskswith fewer irregularities.

Incidentally, a typical conventional photolithographic apparatus effectsoverall patterning by repeating exposure while stepwisely moving aphotosensitive plate to be a mask pattern original plate and an exposurehead relative to each other in directions X and Y. FIG. 6 is afragmentary perspective view of one example of the conventionalphotolithographic apparatus. A photosensitive plate P is set on a stage1 that is moved in a direction Y under control. An exposure head 2 thatprojects a hole pattern of a mask onto the photosensitive plate Pthrough a reduction lens 3 is attached to a plate (not shown) that ismoved in a direction X under control. Accordingly, it is possible toeffect patterning of a mask pattern original plate by repeating exposurewhile stepwisely moving the stage 1 and the exposure head 2 in therespective directions Y and X accurately with a predetermined pitch. Toeffect accurate control of the stepwise movement, an X-directioninterferometer 7 and a Y-direction interferometer 8 are attached to theexposure head 2, and moving mirrors 11 and 12, each constituting a partof the associated interferometer, are attached to the stage 1 inopposing relation to the associated interferometers 7 and 8. Theexposure head 2 is further equipped with mirrors 9 and 10 for directinglight rays which enter and emerge from the associated interferometers 7and 8 toward the respective moving mirrors 11 and 12. The apparatus bodyB, on which the above-described elements are mounted, is provided with alaser light source 4 that oscillates simultaneously light rays of twonear-by frequencies f₁ and f₂ which are in common to the twointerferometers 7 and 8, a beam splitter 5 that splits the light inorder to direct part of the light toward the Y-direction interferometer8, a mirror 6 that directs the remaining light toward the X-directioninterferometer 7, and X- and Y-direction detectors 13 and 14 thatreceive beam light from the associated interferometers 7 and 8 to detecta movement in each direction. FIG. 7 shows the optical arrangement ofeach interferometer. More specifically, the interferometer 7 (8)comprises a polarization beam splitter 15 and a pair of corner cubemirrors 16 and 17 which are cemented to the upper and lower surfaces,respectively, of the polarization beam splitter 15. A quarter-wave plate18 is disposed in front of the reverse surface of the interferometer 7(8) with respect to the surface at the incidence side. The light offrequency f₁ from the laser light source 4 is polarized in parallel tothe plane of FIG. 7, while the light of frequency f₂ is polarized in adirection normal to the plane of the figure. These two light rays enterthe polarization beam splitter 15, and the light of frequency f₁, whichis polarized in parallel to the plane of the figure, passes through thesplit plane and enters the quarter-wave plate 18 where the polarizationis converted into circular polarization. The circularly polarized lightstrikes on the moving mirror 11 (12) to receive Doppler shift Δf andthen enters the quarter-wave plate 18 again, where the circularpolarization is converted into polarization in a direction normal to theplane of the figure. The polarized light is reflected by the split planeto enter the lower corner cube mirror 17 and then returns along anoptical path which is a little offset from the optical path of theincident light. The light is then reflected by the split plane to enterthe quarter-wave plate 18 along a light path which is offset from theprevious optical path, where the polarization is converted into circularpolarization. The circularly polarized light strikes on the movingmirror 11 (12) again to receive Doppler shift Δf, and with Doppler shiftof 2Δf in total, the light enters the quarter-wave plate 18, where it isconverted into light polarized in parallel to the plane of the figure.The light passes through the split plane and emerges from thepolarization beam splitter 15. Meantime, the light of frequency f₂,which is polarized in a direction normal to the plane of the figure, isreflected by the split plane to enter the upper corner cube mirror 16and returns along an optical path which is a little offset from theoptical path of the incident light. The light is reflected by the splitplane again to be output in superposition on the signal of frequency f₁that has received Doppler shift of 2Δf. Accordingly, the amount ofmovement of the photosensitive plate P relative to the exposure head 2can be obtained by taking out Doppler shift 2Δf of the light returningfrom the moving mirror 11 (12) for each direction (Doppler shift may betaken out, for example, by subtracting the beam signal frequency of f₁and f₂ from the beam signal frequency of f₁ ±2Δf and f₂), and totalingthe number of pulses, which are output, for example, one pulse perperiod of Doppler frequency 2Δf. In this way, the movement d is obtainedas being d=N×λ/4 from the relation of Δf=2vnf/c=2vn/λ₀ =2v/λ, wherein: vis the speed of the moving mirror 11 (12); n, the refractive index ofthe air; f, the frequency of laser light; c, the light velocity in avacuum; λ₀, the wavelength in a vacuum; and λ, the wavelength in theair. Accordingly, by counting the number of such pulses, exposure can berepeated with the stage 1 and the exposure head 2 being stepwisely movedaccurately with a predetermined pitch in the respective directions X andY, so that accurate patterning of a mask pattern original plate can beeffected. The same is the case with other examples of thephotolithographic apparatus in which the exposure head moves in the X-Ydirections or the stage having a photosensitive plate mounted thereonmoves in the X-Y directions.

Incidentally, irregularities of shadow mask patterns are considered tobe attributable to irregularities in the arrangement of small holepatterns produced when shadow mask patterns are drawn by aphotolithographic apparatus such as that shown in FIG. 6, but most ofthe irregularities are attributable to instability of the wavelength oflaser light used in a distance measuring system that employs aninterferometer (as will be clear from the above equation d=N×λ/4, achange in the wavelength λ of the laser light makes the actual movementd different for the same count N). Because the wavelength λ in the airchanges with the atmospheric pressure, temperature and humidity, factorsin the instability of the wavelength of the laser light may beconsidered to be 1) the atmospheric pressure, 2) temperature and 3)humidity of the air in the optical path where the laser light passes. Inthe case of an electron beam lithographic apparatus, the instability ofwavelength can be eliminated by placing the optical path of laser lightin a vacuum, but in the case of a photolithographic apparatus, which islarge in size, the whole apparatus cannot be placed in a high-vacuumsystem from the viewpoint of cost and it is therefore necessary to makereal-time correction for a change in wavelength due to 1) theatmospheric pressure, 2) temperature and 3) humidity of the air in theoptical path of laser light. FIGS. 8 and 9 show examples of positioncontrol system designed for this purpose.

In the example shown in FIG. 8, a target position to which the exposurehead 2 and the photosensitive plate P are to be positioned relative toeach other is input from a target position input device 20 for eachexposure operation. In actual practice, target positions which havepreviously been programmed are inputted successively. Pulse signals froman interferometric measuring device 22, which comprises aninterferometer such as that shown in FIG. 7 and a circuit that outputs aDoppler shift obtained therefrom in the form of pulses, are subjected toaddition or subtraction in a pulse counter 23. As described above, thepulse count value represents a relative movement of the exposure head 2and the photosensitive plate P, that is, the position of an X-Y stagesystem 21. Incidentally, there are provided a barometer 24 that detectsthe pressure of an atmosphere where the photolithographic apparatus isplaced, a thermometer 25 that detects the atmospheric temperature, and ahygrometer 26 that detects the humidity, and detected signals from thesedetectors are sent to a laser wavelength computing device 27 to obtainthe actual wavelength λ in the air in the present state, which isobtained by correcting the wavelength λ₀ in a vacuum, with reference toa table previously stored therein (the wavelength may be obtainedaccording to Owen's equation that expresses the relationship between theatmospheric pressure, temperature and humidity on the one hand and thewavelength on the other; see Keiei Kudo, "Charts of Basic PhysicalProperties--Mainly Spectral Properties," Kyoritsu Shuppan K. K., May 15,1972, p. 138). The count of the pulse counter 23 is multiplied by thewavelength λ given by the laser wavelength computing device 27 in amultiplier 28 to obtain the present position of the X-Y stage system 21(if a distance measuring device that outputs 1 pulse for each movementof 1/n wavelength is employed, the count is multiplied by λ/n). Adifference between the target position that is input from the targetposition input device 20 and the present position that is corrected asdescribed above is obtained by a subtracter 29 for calculating aposition error. The error signal thus obtained is amplified in anamplifier 30 and then applied to a servomotor 31 that moves the X-Ystage system 21 in the directions X and Y, thereby moving the exposurehead 2 and the photosensitive plate P to the target relative position,that is, the target position that has been corrected for an error in themeasured value due to a wavelength change in the distance measuringsystem, and thus enabling exposure to be repeated while stepwiselymoving the exposure head 2 and the photosensitive plate P with highaccuracy. It should be noted that the control of movement is startedafter the moving mirrors 11 and 12, which are associated with theinterferometers 7 and 8, have been returned to their origins (referencepositions) and the counter 23 has been reset to zero at this position bya resetting device 32. The example that is shown in FIG. 9 is amodification of the control system shown in FIG. 8, in which a targetposition that is input from the target position input device 20 isdivided in a divider 33 by the actual wavelength λ that is output fromthe laser wavelength computing device 27, thereby quantizing the targetposition in advance, and a comparison is made between the target digitalvalue obtained by the quantization and the digital value representativeof the present position which has been cumulated in the pulse counter23, thereby generating an error signal. This system performs essentiallythe same function as that of the system shown in FIG. 8.

However, even if a photolithographic apparatus is arranged such that theaccuracy in positioning the exposure head 2 and the photosensitive plateP relative to each other is independent of the conditions of theatmosphere by utilizing the position control system shown in FIG. 8 or9, irregularities still occur due to a lowering in the positionalaccuracy of small hole patterns which should be arranged regularly.FIGS. 10(a) and 10(b) show one example of such irregularities. In thisexample, first and second mask patterns (see FIG. 10(b)) were written insuccession, spending more than 1 day, in an atmosphere where the airtemperature was substantially constant but the air pressure was variable(see FIG. 10(a)). Linear irregularities occurred when the atmosphericpressure changed suddenly during the process for the second maskpattern.

For example, if a photolithographic apparatus such as that shown in FIG.6 employs a distance measuring system that comprises interferometershaving an optical system such as that shown in FIG. 7, the movement ofthe exposure head 2 is measured from a measurement start point (origin)which is selected in the directions of movement of the moving mirrors 11and 12. This is because a distance measuring system that comprisesMichelson interferometers such as that shown in FIG. 7 is designed tomeasure a relative movement. The measurement start point must besomewhat spaced apart from the polarization beam splitter 15 across theair in the distance measuring direction from the viewpoint of themechanical arrangement. This will also be understood from the fact thatthe moving mirrors 11 and 12 cannot completely be brought into contactwith the associated interferometers 7 and 8. Upon the actual positioncontrol of the exposure head 2, the movement control to the desiredtarget position is started after the exposure head 2 has been returnedto the measurement start point (origin) and the controller has beenreset by the resetting device 32, as shown in FIGS. 8 and 9.

Various examinations have revealed that the above-describedirregularities in shadow mask patterns occur due to a wavelength changein the air in the optical path between the origin and the polarizationbeam splitter (this optical path will hereinafter be referred to as"dead path"). This will be explained below in more detail. Specifically,the distance of this dead path is on the order of 0.2 to 0.3 m, and apitch error of about 0.1 μm occurs irregularly. More specifically, inthe conventional controllers shown in FIGS. 8 and 9, an origin is set,as shown in FIGS. 11(a) and 11(b), and the controller is reset withrespect to this point (see FIG. 11(a)). Then, a target position isinput, and the exposure head 2 is moved by effecting position control bythe servo-system shown in FIG. 8 or 9 (see FIG. 11(b)). In the priorart, however, correction is made only for a wavelength change in thepath between the origin and the moving mirror 11 (12), but no correctionis made for a wavelength change in the dead path between thepolarization beam splitter 7 (8) and the origin. For this reason, awavelength change in this dead path causes the count of pulses to changecorrespondingly, so that no accurate movement control can be effectedand the above-described irregularities occur in the resulting shadowmask pattern.

Under these circumstances, one embodiment of the photolithographicapparatus according to the present invention adopts a position controlsystem such as that shown in FIG. 12 in order to correct a wavelengthchange in the dead path. More specifically, a target position which ismeasured from the origin and where the exposure head 2 should bepositioned is input from a target position input device 20 for eachexposure operation (in actual practice, target positions which havepreviously been programmed are input successively). Pulse signals froman interferometric measuring device 22, which comprises aninterferometer such as that shown in FIG. 7 and a circuit that outputs aDoppler shift obtained therefrom in the form of pulses, are subjected toaddition or subtraction in a pulse counter 23. The pulse counter 23 isreset to zero by a resetting device 32 when an X-Y stage system 21 isreturned to the origin at the time of starting an exposure operation.Accordingly, the pulse count value represents a movement of the exposurehead 2 from the origin, that is, the position of the X-Y stage system 21relative to the origin. In addition, there are provided a barometer 24that detects the pressure of an atmosphere where the photolithographicapparatus is placed, a thermometer 25 that detects the atmospherictemperature, and a hygrometer 26 that detects the humidity, and detectedsignals from these detectors are sent to a laser wavelength computingdevice 27 to obtain the actual wavelength λ in the air in the presentstate, which is obtained by correcting the wavelength λ₀ in a vacuum,with reference to a table previously stored therein, in the same way asin the prior art (see FIG. 8). It should be noted that the wavelengthmay be obtained according to the above-mentioned Owen's equation, whichexpresses the relationship between the atmospheric pressure, temperatureand humidity on the one hand and the wavelength on the other. Thewavelength λ_(S) in the air at the time when the pulse counter 23 isreset is stored in a register 37 from the laser wavelength computingdevice 27 on the basis of a signal from the resetting device 32. In thisembodiment, a dead path input device 34 is provided to give the lengthof a dead path (in actual practice, it is read from a memory). The deadpath length that is output from the dead path input device 34 is dividedin a divider 35 by the wavelength λ_(S) at the time of resetting to theorigin, stored in the register 37, and the resulting quotient (i.e., adigital value reduced by the wavelength λ_(S) in the dead path at thetime of resetting) is added to the count of the pulse counter 23 in anadder 36. The resulting sum is multiplied by the wavelength λ in the airat the present time, which is output from the laser wavelength computingdevice 27, in a multiplier 28 to obtain the actual present position ofthe X-Y stage system 21 (i.e., the position that is measured from thepolarization beam splitter). Then, the dead path length output from thedead path input device 34 is subtracted from the signal representativeof the present position in a subtracter 38, thereby obtaining thepresent position of the X-Y stage system 21 measured from the origin,which has been corrected for wavelength changes in the dead path and theoptical path between the origin and the present position. A differencebetween the target position that is input from the target position inputdevice 20 and the present position that is corrected as described aboveis obtained by a subtracter 29 for calculating a position error. Theerror signal thus obtained is amplified in an amplifier 30 and thenapplied to a servomotor 31 that moves the X-Y stage system 21 in thedirections X and Y, thereby moving the exposure head 2 to the targetposition, that is, the target position that has been corrected for anerror in the measured value due to wavelength changes in all the spacesin the distance measuring system, and thus enabling exposure to berepeated while stepwisely moving the exposure head 2 and thephotosensitive plate P with high accuracy.

The operation of the above-described controller will be explained bymathematics. Assuming that a target position that is input from thetarget position input device 20 is A and a dead path length that isoutput from the dead path input device 34 is D and that the X-Y stagesystem 21 is at rest at the target position after reaching there withoutan error by an operation of the feedback control system shown in FIG.12. The register 37 has been stored with the wavelength λ_(S) at thetime when the X-Y stage system 21 was returned to the origin and thepulse counter 23 was reset to zero. In addition, the multiplier 28 hasbeen supplied with the wavelength λ in the air at the present time fromthe laser wavelength computing device 27. In this state, the pulsecounter 23 ought to have counted (A+D)/λ-D/λ_(S) pulses. Since a digitalvalue for D/λ_(S) is output from the divider 35, a digital value for(A+D)/λ is output from the adder 36. This is multiplied by λ in themultiplier 28 to output a value for (A+D), that is, a distance from thepolarization beam splitter 15 to the moving mirror 11 (12). The deadpath length D is subtracted from the distance (A+D) in the subtracter 38to obtain the target position A. In other words, even if the wavelengthchanges from λ_(s) to λ, employment of the above-described controlsystem enables the wavelength change in the dead path to be alsocorrected and hence allows the X-Y stage system 21 to be movedaccurately to the target position by feedback control. In the prior artthat is not provided with the dead path input device 34, the divider 35,the adder 36, the register 37 and the subtracter 38, as in FIG. 8, thevalue that is output from the subtracter 38 under the same conditions isA-D x λ/λ_(s), so that the X-Y stage system 21 is moved to an erroneousposition by the feedback loop, although it has reached the targetposition A without an error. Accordingly, with the above-describedposition controller of the present invention, even if there is a changein the atmospheric pressure, temperature or humidity of thephotolithographic apparatus, no irregularities will occur in theresulting shadow mask.

The controller shown in FIG. 12 may also be modified in the same way asin the case of the prior art that is shown in FIG. 9. More specifically,as shown in FIG. 13, a target position, which is obtained by addingtogether a target position based on the origin and a dead path length inan adder 39, is divided in a divider 33 by the actual wavelength λoutput from the laser wavelength computing device 27 to quantize thetarget position in advance, and the target digital value obtained by thequantization is compared with a value that is obtained by adding adigital value reduced by the wavelength λ_(s) in the dead path at thetime of resetting to the count of the pulse counter 23, that is, adigital value which is representative of the present position, therebygenerating an error signal. The operation of this modification isessentially the same as in the case of the controller shown in FIG. 12.

Incidentally, the embodiments shown in FIGS. 12 and 13 are arranged suchthat the whole of a photolithographic apparatus such as that shown inFIG. 6 is placed in the air and patterns are drawn by controlling therelative position of the stage 1 and the exposure head 2. However, thearrangement may be such that only the stage 1, the exposure head 2 andthe moving mirrors 11 and 12 are accommodated in a vacuum chamber 40,while the interferometers 7 and 8 are disposed in the air, as shownschematically in FIG. 14, so that light that travels toward the movingmirror 11 (12) through the interferometer 7 (8) is introduced through awindow 41 provided in the vacuum chamber 40. In such a case, awavelength change occurs only in a section D' of the dead path D whichextends between the beam splitter and the window 41. In this case, thedead path length that is handled in the controllers shown in FIGS. 12and 13 is not D but D'.

Although in the foregoing embodiments the resetting device 32 thatresets the pulse counter 23 when the X-Y stage system 21 is moved to theorigin is assumed to be a manually operated, it should be noted that anyknown device, for example, a mechanical, optical, electric, magnetic orphotoelectric device, may be employed as long as it is adapted to send asignal to a reset terminal of the pulse counter 23 when the X-Y stagesystem 21 has reached a predetermined origin, by automatically detectingthis fact.

Although the foregoing description has been made about some embodimentsof an exposure head position controller of a photolithographic apparatusfor use in the production method according to the present invention, itshould be noted that the present invention is not necessarily limited tothe described embodiments and that various modifications and changes maybe imparted thereto. For example, the arrangement may be such that, whenthe X-Y stage system 21 is moved to the origin, the pulse counter 23 isnot reset, but a value that is output from the divider 35 is preset tothe pulse counter 23. In addition, the present invention may be appliednot only to a photolithographic apparatus for forming shadow maskpatterns but also to other types of apparatus, for example, aphotolithographic apparatus that employs a Michelson interferometer toeffect position control.

As has been described above, the photolithographic apparatus for use inthe method of producing master and working pattern plates for etchingaccording to the present invention is provided with a memory means forstoring the wavelength in the air at the time of resetting the count ofthe counter to zero when the moving mirror is moved to the origin, andit is arranged such that a value that is obtained by dividing thedistance between the beam splitter and the origin by the wavelengthstored in the memory means is added to the value of the counter, and theresulting sum is multiplied by the wavelength in the air at the presenttime, and further the distance between the beam splitter and the originis subtracted from the value obtained by the multiplication, and theposition of the moving mirror is feedback-controlled on the basis of thedifference between the value obtained by the subtraction and the targetposition of the moving mirror. Accordingly, even if the wavelengthchanges due to a change in the pressure, temperature or humidity of theair in the dead path between the beam splitter and the origin, theposition error due to this change is corrected. Thus, even if there is achange in the atmospheric pressure, temperature or humidity of thephotolithographic apparatus for forming shadow mask patterns, theresulting shadow mask has no irregularities, which would otherwise begenerated due to a lowering in the positional accuracy of small holepatterns which should be arranged regularly.

What we claim is:
 1. A photolithographic apparatus which is arranged toprepare individual pattern date required for an etching pattern platecomprising an alignment mark pattern, a hole pattern, a frame pattern,etc., prepare single synthetic pattern data by subjecting each of saidindividual pattern data to a logical operation, and effect continuousand collective exposure to a photosensitive glass plate by use of saidsynthetic pattern data to form a latent image corresponding to saidsynthetic pattern data, and which has a device that controls themovement of a moving mirror of a Michelson interferometer from itsorigin by counting the number of interference fringes, or Doppler shiftfrequency, from said interferometer with a counter, thereby controllingthe relative position of an exposure head and a photosensitive plate,wherein the improvement comprises a position controller that sets theorigin of said moving mirror at a distance from a beam splitter of saidMichelson interferometer, moves said moving mirror to the origin toreset the count of said counter to zero and then feedback-controls theposition of said moving mirror on the basis of the difference between avalue obtained by multiplying the count of said counter by thewavelength in the air at the present time and a target position of saidmoving mirror, said position controller having a memory means forstoring the wavelength in the air at the time when said moving mirror ismoved to the origin and said counter is reset to zero, and said positioncontroller being arranged such that a value obtained by dividing thedistance between said beam splitter and the origin by the wavelengthstored in said memory means is added to the count of said counter; theresulting sum is multiplied by the wavelength in the air at the presenttime; the distance between said beam splitter and the origin issubtracted from the resulting product; and the position of said movingmirror is feedback-controlled on the basis of the difference between theresult of said subtraction and a target position of said moving mirror.2. A photolithographic apparatus which is arranged to prepare individualpattern data required for an etching pattern plate comprising analignment mark pattern, a hole pattern, a frame pattern, etc., preparesingle synthetic pattern data by subjecting each of said individualpattern data to a logical operation, and effect continuous andcollective exposure to a photosensitive glass plate by use of saidsynthetic pattern data to form a latent image corresponding to saidsynthetic pattern data, and which has a device that controls themovement of a moving mirror of a Michelson interferometer from itsorigin by counting the number of interference fringes, or Doppler shiftfrequency, from said interferometer with a counter, thereby controllingthe relative position of an exposure head and a photosensitive plate,wherein the improvement comprises a position controller that sets theorigin of said moving mirror at a distance from a beam splitter of saidMichelson interferometer, moves said moving mirror to the origin toreset the count of said counter to zero and then feedback-controls theposition of said moving mirror on the basis of the difference betweenthe count of said counter and a value obtained by dividing a targetposition of said moving mirror by the wavelength in the air at thepresent time, said position controller having a memory means for storingthe wavelength in the air at the time when said moving mirror is movedto the origin and said counter is reset to zero, and said positioncontroller being arranged such that the distance between said beamsplitter and the origin is added to a target position of said movingmirror; the resulting sum is divided by the wavelength in the air at thepresent time; and the position of said moving mirror isfeedback-controlled on the basis of the difference between the resultingquotient and a value that is obtained by adding to the count of saidcounter a value obtained by dividing the distance between said beamsplitter and the origin by the wavelength stored in said memory means.